The present invention relates to gear pumps and liquid ejection apparatuses employing such gear pumps.
Conventionally, gear pumps are configured relatively simply and thus advantageous with respect to other types of pumps. As such gear pumps, for example, the gear pump 100 of FIG. 11 is known. The gear pump 100 includes a housing 101 in which an accommodating chamber 102 is defined for accommodating a drive gear 103 and a driven gear 104. An opening for the accommodating chamber 102 in the housing 101 is sealed by a non-illustrated seal plate. The upper surfaces of the drive gear 103 and the driven gear 104 are held in contact with the seal plate in a slidable manner. If the drive gear 103 is rotated through rotation of a drive shaft 105, the driven gear 104 is rotated as driven by the drive gear 103. In this state, the liquid retained in the suction chamber 110 defined in the accommodating chamber 102 is moved to the space defined by each gear groove of the gears 103, 104 and the inner walls of the accommodating chamber 102. The liquid is eventually discharged into a discharge chamber 112. The liquid is continuously introduced into the discharge chamber 112, which is defined in the accommodating chamber 102, through rotation of the gears 103, 104. The pressure in the discharge chamber 112 thus becomes higher than the pressure in the suction chamber 110.
If the gap between the gears 103, 104 and the seal plate is relatively large, the liquid leaks through the gap and is recirculated from the discharge chamber 112 under relatively high pressure to the suction chamber 110 under relatively low pressure. It is thus necessary to minimize the gap between the gears 103, 104 and the seal plate. To meet this need, a gear pump in which a plate spring is deployed between the bottom surface of the accommodating chamber 102 and the gears 103, 103 has been proposed (as described in, for example, Japanese Laid-Open Patent Publication No. 8-093657). The plate spring urges each of the gears 103, 104 toward the seal plate or the housing.
However, if the gears are pressed by the plate spring against the seal plate, relatively great friction torque or viscous load torque is produced when the gears slide along the seal plate or the housing. This causes a relatively great load to act on the drive source of the gear pump 100, which is a problem.